The long term goal of the research program described is to understand the mechanisms and genic control of mitotic and meiotic recombination. The specific aims of the experiments described are: (1) to establish the rules of mitotic exchange with respect to intragenic and intergenic events; (2) to characterize the genic control of chromosomal recombination with respect to mitosis specific, meiosis specific and common functions and, (3) to test the Meselson Radding model of genetic recombination as it applies to mitotic and meiotic recombination. In the context of these aims temperature sensitive hypo-rec and hyper-rec mutants will be isolated and characterized with respect to their mitotic and meiotic phenotypes and the order of function of the rec gene products involved.